A senior Sudanese opposition leader detained since December has been released, as thousands in Khartoum went on strike in support of protests against President Omar Al Bashir. Members of the Sudanese Congress Party said on Tuesday the chief of the party Omar El Digeir was arrested days after protests erupted on December 19. "But 40 other party leaders are still in detention," the party said in a statement. Mr El Digeir's party called for the strike that left the capital Khartoum and twin city of Omdurman empty on Tuesday, Associated Press reported. It also called for street demonstrations later in the day. Sudanese authorities in December launched a widespread crackdown to curb protests as they spread into nationwide demonstrations against Mr Al Bashir, who came to power in a coup in 1989. At least 51 people have been killed in clashes between protesters and forces, according to Human Rights Watch. Officials put the number at 31. On Friday President Al Bashir <a href="https://www.thenational.ae/world/mena/sudan-s-omar-al-bashir-steps-down-as-party-head-after-months-of-protests-1.832216">stepped down as chairman of his party</a>, delegating to his deputy instead. In February he declared a year-long state of emergency to quell the protests after the crackdown, in which children and medics are reported to have been killed, failed to suppress the movement. He also dissolved the federal and provincial governments, and appointed 16 army officers and two security officers from the feared National Intelligence and Security Service as governors of the country's 18 provinces. Protesters accuse the president's administration of mismanaging the country's economy and have called on the 75-year-old president to step down. Mr Al Bashir has remained defiant, banning unauthorised rallies and setting up special courts to investigate breaches during the state of emergency. Hundreds of protesters have been arrested and put on trial at emergency courts, eight were sentenced to jail, with four handed five-year prison terms each, the official SUNA news agency said.